The Cr plus 2 - Cr plus 3 oxidation is being used to fix Cr to the metal-binding sites of yeast enolase and tRNA so that the role(s) of the different binding sites can be assessed. The kinetically observed transformations of human erythrocyte pyruvate kinase, that result from oxidation, hexosediphosphate binding and incubation with substrates are being studied to define them in physical terms and to provide insight into their physiological regulatory function.